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Thermal conductivity of gas by pulse injection techniques using specific thermal conductivity detector (TCD)

Veses, Renato Cataluna; Silva, Rosângela da; Menezes, Eliana Weber de; Samios, Dimitrios
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
ENG
Relevância na Pesquisa
696.02875%
Este artigo apresenta um procedimento para determinar a condutividade térmica de gases através de injeção por pulso, utilizando um detector de condutividade térmica (TCD). As medidas foram efetuadas à 323K e pressão atmosférica, com um sensor de filamento de tungstênio de 160 Ω. Através de aproximações bem definidas, foi possível transformar uma equação de segunda ordem não-linear, que descreve a saída do sensor como uma função de condutividade térmica e calor específico a volume constante (Cv), em uma equação linear de primeira ordem. De acordo com esta equação, o sinal elétrico do sensor, elevado ao quadrado e integrado em função do tempo, multiplicado pelo Cv, é proporcional a razão do Cv pela condutividade térmica. Os resultados experimentais obtidos com os gases Ar, N2, O2, CH4, CO2, C2H4, C3H6 e i-C4H8 estão de acordo com o modelo teórico proposto e a correlação de linearidade confirma a validade do método proposto.; This paper presents a procedure to determine the thermal conductivity of gases by pulse injection, using a thermal conductivity detector (TCD). The measurements are taken at 323K and atmospheric pressure with a 160 Ω tungsten filament sensor. Under well defined approximations the original nonlinear second order equation...

Effect of maltodextrin on the freezing point and thermal conductivity of uvaia pulp (Eugenia piriformis Cambess)

Villa-Vélez, Harvey Alexander; Telis-Romero, Javier; Higuita, Diana Maria Cano; Telis, Vânia Regina Nicolletti
Fonte: Editora da Universidade Federal de Lavras (UFLA) Publicador: Editora da Universidade Federal de Lavras (UFLA)
Tipo: Artigo de Revista Científica Formato: 78-85
ENG
Relevância na Pesquisa
690.6938%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 09/13033-9; O ponto de início de congelamento (FPD) da polpa de uvaia com e sem aditivos - 10, 16, 22 e 28% de maltodextrina (MD), foi medido por um aparelho simples, que consiste de duas seções principais: um vaso de congelamento e um sistema de aquisição de dados. A condutividade térmica foi calculada em função da fração de água congelada e da temperatura, usando um aparelho cilíndrico coaxial duplo. Foram empregadas equações polinomiais para descrever o comportamento do ponto inicial de congelamento e da condutividade térmica. Abaixo do ponto de congelamento, a condutividade térmica foi fortemente afetada pela fração de água congelada e pela temperatura. Equações simples em termos da fração de água congelada e da temperatura podem ser ajustadas aos dados experimentais no cálculo do início do ponto de congelamento e da condutividade térmica.; The freezing point depression (FPD) of uvaia pulp with and without additives - 10, 16, 22 and 28% of maltodextrin (MD), was measured using a simple apparatus consisting of two major sections: a freezing vessel and a data acquisition system. The thermal conductivity of the pulps was also investigated as a function of the frozen water fraction and temperature using a coaxial dual-cylinder apparatus. Above the initial freezing point...

Freezing point and thermal conductivity of tropical fruit pulps: Mango and papaya

Telis, V. R N; Telis-Romero, J.; Sobral, P. J A; Gabas, A. L.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 73-84
ENG
Relevância na Pesquisa
692.90586%
The freezing point depression of mango and papaya pulps was measured by using a simple apparatus, consisting of two major sections: a freezing vessel and a data acquisition system. The thermal conductivity of both pulps as a function of frozen water fraction and temperature was also investigated by using a coaxial dual-cylinder apparatus. Thermal conductivity above the initial freezing point was well fitted by polynomial equations. Below the freezing point, the thermal conductivity was strongly affected by both the frozen water fraction and temperature. Simple equations in terms of frozen water fraction and temperature could be fitted to the experimental data of freezing point depression and thermal conductivity.

Sintering of porous alumina obtained by biotemplate fibers for low thermal conductivity applications

Delbrücke, Tiago; Gouvêa, Rogério A.; Moreira, Mário L.; Raubach, Cristiane W.; Varela, José Arana; Longo, Elson; Gonçalves, Margarete R.F.; Cava, Sergio
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1087-1092
ENG
Relevância na Pesquisa
691.3688%
In this research report, a sintering process of porous ceramic materials based on Al2O3 was employed using a method where a cation precursor solution is embedded in an organic fibrous cotton matrix. For porous green bodies, the precursor solution and cotton were annealed at temperatures in the range of 100-1600°C using scanning electron microscopy (SEM) and thermogravimetric (TG) analysis to obtain a porous body formation and disposal process containing organic fibers and precursor solution. In a structure consisting of open pores and interconnected nanometric grains, despite the low porosity of around 40% (calculated geometrically), nitrogen physisorption determined a specific surface area of 14m2/g, which shows much sintering of porous bodies. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analytical methods revealed a predominant amount of α-Al2O3 in the sintered samples. Thermal properties of the sintered Al2O3 fibers were obtained by using the Laser Flash which resulted in the lower thermal conductivity obtained by α-Al2O3 and therefore improved its potential use as an insulating material. © 2012 Elsevier Ltd.

Avaliação do congelamento de solução modelo por condutividade termica.; Freezing evaluation of model solution by thermal conductivity.

Lena Soledad Monzon Davila
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 31/07/2007 PT
Relevância na Pesquisa
695.2437%
As propriedades termofisicas dos alimentos são requeridas para o cálculo de tempo de processamento em projetos de equipamentos para a indústria de alimentos. Os processos de congelamento exigem dados precisos das propriedades térmicas do produto, tais como condutividade térmica, fração de gelo, calor específico e entalpia. A necessidade do conhecimento do comportamento destas propriedades tem levado ao desenvolvimento de alguns modelos matemáticos para suas predições. A condutividade térmica dos alimentos é uma propriedade fortemente dependente da composição química e da temperatura do alimento. Neste trabalho compararam-se os resultados experimentais de condutividade térmica de soluções modelo congeladas em três diferentes velocidades de congelamento, utilizando o método da sonda linear de aquecimento, com os obtidos pelo modelo matemático "Maxwell-Eucken" ou disperso como função da fração de gelo contida nos alimentos. Foi obtida uma divergência com o modelo por não considerar a velocidade de congelamento. Determinou-se que a condutividade térmica é uma propriedade termofísica diretamente proporcional ao aumento da velocidade de congelamento Os valores de condutividade térmica das amostras foram calculados através da inclinação obtida da regressão linear determinada pelo perfil do logaritmo natural do tempo versus temperatura. Os resultados da condutividade térmica foram correlacionados com as velocidades de congelamento e com a fração de gelo...

Thermal conductivity and thermal diffusivity of cores from a 26 meter deep borehole drilled in Livingston Island, Maritime Antarctic

Correia, António; Vieira, Gonçalo; Ramos, Miguel
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
694.28766%
During the month of January of 2008 a borehole (Permamodel-Gulbenkian 1 — PG1) 26 m deep was drilled on the top of Mount Reina Sofia (275 m a.s.l.) near the Spanish Antarctic Station of Livingston Island, South Shetland Islands. Cores from1.5 mto about 26mdeepwere collected formeasuring several physical properties. The objective of the present work is to report the values of the thermal conductivity and the thermal diffusivity that were measured in the cores fromthe borehole and the heat production thatwas estimated for the geological formations intercepted by it. Seven coreswere selected to measure the thermal conductivity and the thermal diffusivity. The measured values for the thermal conductivity vary from2.6W/mK to 3.3 W/mKwhile the measured values for the thermal diffusivity vary from 1.1×10−6 m2/s to 1.6×10−6 m2/s. Both thermal conductivity and thermal diffusivity, on average, show a slight increase with depth. Average heat production was also estimated for two portions of the borehole: one from2 to 12mand the other from12 to 25 m. A gamma-ray spectrometer was used to estimate the concentrations of uranium, thorium, and potassium of the cores, from which the heat production per unit volume was calculated. The estimated heat production for the first half of the borehole is 2.218 μW/m3 while for the second half it is 2.173 μW/m3; these heat production values are compatiblewith acidic rock types. Porosity and density were also estimated for the same cores.

Thermal conductivity of gas by pulse injection techniques using specific thermal conductivity detector (TCD)

Cataluña,Renato; Silva,Rosângela da; Menezes,Eliana W.; Samios,Dimitrios
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2004 EN
Relevância na Pesquisa
696.02875%
This paper presents a procedure to determine the thermal conductivity of gases by pulse injection, using a thermal conductivity detector (TCD). The measurements are taken at 323K and atmospheric pressure with a 160 omega tungsten filament sensor. Under well defined approximations the original nonlinear second order equation, which describes the sensors output, as a function of thermal conductivity and constant volume specific heat was transformed into a linear first order equation. According to this equation the time integrated, second order sensors electrical output signal, multiplied by the constant volume heat capacity is proportional to the constant volume heat capacity, divided by the thermal conductivity. The experimental results obtained with Ar, N2, O2, CH4, CO2, C2H4, C3H6 and i-C4H8 gases are in good agreement with the proposed theoretical model and the linearity correlation confirms the validity of the proposed method.

Estimation of effective thermal conductivity enhancement using foam in heat exchangers based on a new analytical model

Haghighi,Maryam; Kasiri,Norollah
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2010 EN
Relevância na Pesquisa
698.7849%
Thermal performance of open-cell metal foam has been investigated under low Reynolds number by comparing the heat transfer coefficient and thermal conductivity for the flow through a packed channel of high porosity metal foam to that of an open channel. In the case of Al-Air at porosity 0.971, the ratio of heat transfer coefficients is estimated to be 18.5 when the thermal conductivity ratio of foam matrix to fluid conductivity is 130. This demonstrates that the useusing of foam in the structure of conventional air coolers increases effective thermal conductivity, heat transfer coefficient and thermal performance considerably. To overcome the drawbacks of previous models, a new model to describe the effective thermal conductivity of foam was developed. The model estimates effective thermal conductivity based on a non-isotropic tetrakaidecahedron unit-cell and is not confined only to isotropic cases as in previous models. Effective thermal conductivity is a function of foam geometrical characteristics, including ligament length (L), length of the sides of horizontal square faces (b), inclination angle that defines the orientation of the hexagonal faces with respect to the rise direction (θ), porosity, size, shape of metal lump at ligament intersections and heat transfer direction. Changing dimensionless foam ligament radius or height (d) from 0.1655 to 0.2126 for Reticulated vitreous foam -air (RVC-aAir) at θ=π/4 and dimensionless spherical node diameter (e) equal to 0.339...

Effect of maltodextrin on the freezing point and thermal conductivity of uvaia pulp (Eugenia piriformis Cambess)

Villa-Vélez,Harvey Alexander; Telis-Romero,Javier; Higuita,Diana Maria Cano; Telis,Vânia Regina Nicolletti
Fonte: Editora da Universidade Federal de Lavras Publicador: Editora da Universidade Federal de Lavras
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2012 EN
Relevância na Pesquisa
690.6938%
The freezing point depression (FPD) of uvaia pulp with and without additives - 10, 16, 22 and 28% of maltodextrin (MD), was measured using a simple apparatus consisting of two major sections: a freezing vessel and a data acquisition system. The thermal conductivity of the pulps was also investigated as a function of the frozen water fraction and temperature using a coaxial dual-cylinder apparatus. Above the initial freezing point, thermal conductivity fitted the polynomial equations well. Below the freezing point, thermal conductivity was strongly affected by both the frozen water fraction and the temperature. Simple equations in terms of the frozen water fraction and temperature could be fitted to the experimental data for freezing point depression and thermal conductivity.

Analysis of effective thermal conductivity for mineral cast material structures with varying epoxy content using TPS method

Selvakumar,A.; Mohanram,P. V.
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2013 EN
Relevância na Pesquisa
694.7654%
Conventionally, cast iron is the material used for high speed machine tool structures. As an alternate material to improve the structural properties, composite materials are being used, which are known to exhibit excellent thermal and mechanical properties. While selecting an alternate material, thermal conductivity is an important thermo physical property of the material that should be studied. A resin composite material has a lesser thermal conductivity and its thermal properties vary with the composition of the mixture. A material with lower thermal conductivity will have higher heat concentration within the structure, which may result in structural deformation. In this analysis, epoxy granite, a material which is tested to exhibit excellent mechanical properties has been selected to study its thermal properties. Tests are carried out using Transient Plane Source (TPS) method, on eight samples with varying volume fraction of epoxy content in the range 10-24%. It is observed that, the effective thermal conductivity decreases with an increase in epoxy resin content in the mixture because the resin content increases interfacial resistance between particles. Hence, lower epoxy content in the mixture that maximizes the effective thermal conductivity while maintaining good mechanical properties is to be selected.

Effect of High-Temperature Aging on the Thermal Conductivity of Nanocrystalline Tetragonal Yttria-stabilized Zirconia

Clarke, David R.; Limarga, Andi M.; Shian, Samuel; Baram, Mor
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
693.6605%
The thermal conductivity of yttria-stabilized zirconia (YSZ) thermal barrier coatings increases with high-temperature aging. This common observation has been attributed to the densification of the coatings as porosity sinters out and pores and cracks spheroidize to minimize their surface energy. We show that the thermalconductivity of fully-dense 3 mol. % Y(_{2})O(_{3}) stabilized zirconia (3YSZ) also increases with high-temperature aging, indicating that densification and pore shape changes alone are not responsible for all the observed increase in thermalconductivity of coatings. Instead, there are also increases due to a combination of phase separation and grain growth. The increase in thermal conductivity can be described by a Larson–Miller parameter. It is also found that the increase in thermal conductivity with aging is greatest when measured at room temperature and decreases with increasing measurement temperature. Measured at 1000 °C, the thermal conductivity of zirconia is almost temperature independent and the changes in thermal conductivity with aging are less than 15%, even after aging for 50 h at 1400 °C.; Physics

Thermal conductivity of milk with different levels of moisture and fat: experimental measures and prediction models; Condutividade térmica de leites com diferentes teores de umidade e gordura: medidas experimentais e modelos de predição

Fonte: Universidade Estadual de Londrina Publicador: Universidade Estadual de Londrina
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
690.6665%
Thermal conductivity is one of the most influential properties affecting the pasteurization of milk and is highly dependent on the milk composition and the temperature used in the process. The purpose of this work was to model the thermal conductivity of milk with a moisture content from 88.3 to 91.2% and fat content from 0 to 3.5% from 20 to 80°C. For milk with a lower moisture percentage, the experimental conductivity ranged from 0.560 to 0.637 W m -1 K -1 , and for those samples with a higher moisture percentage, conductivity ranged from 0.584 to 0.652 W m -1 K -1 . Three theoretical predictive models, series, parallel and Maxwell-Eucken, which use food composition data, were tested, and polynomial functions were fit to model the behavior of this property as a function of moisture and fat content. The results showed that thermal conductivity values are linearly dependent on the moisture content and inversely dependent on the fat content. Among the models, the parallel model was the best fit to the experimental data with a maximum error of 2.7%.

Relationship between the thermal conductivity and rheological behavior of acerola pulp: effect of concentration and temperature

Fonte: Swiss Society of Food Science and Technology Publicador: Swiss Society of Food Science and Technology
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
692.9183%
This study aimed to evaluate the thermal conductivity and rheological behavior of acerola pulp at concentrations of 5.5, 7.5, 9.5, 11.5 and 13.5 Brix and temperatures of 20, 30, 40, 50 and 60 C. Among the models used to determine conductivity, Maxwell-Eucken was used for data acquisition. Linear equations were fitted to evaluate the influences of concentration and temperature on the thermal conductivity of the pulp. The pulp structure, particle sizes and relation between insoluble and soluble solids were also discussed. The rheological behavior, specifically apparent viscosity versus shear rate, was influenced by both the soluble solids content and the temperature. Among the mathematical models used to test the fit of the experimental data, the HerscheleBulkley model provided the best statistical adjustments and was then used to determine the rheological parameters. Apparent viscosity was correlated with temperature by the Arrhenius equation. Acerola pulps were shear thinning and thermal conductivity increases with viscosity decreasing with increasing temperature. The structures and concentrations had an impact upon the effective thermal conductivity. The temperature and concentration values have been fixed and equation expressing conductivity as a function of apparent viscosity was proposed...

WFS-FA-EPS 填料导热系数试验研究; Thermal conductivity of WFS-FA-EPS fills

Deng, A.; Yu, Y.; Wang, H.
Fonte: Editorial Office of Chinese Journal of Geotechnical Engineering Publicador: Editorial Office of Chinese Journal of Geotechnical Engineering
Tipo: Artigo de Revista Científica
Publicado em //2010 ZH
Relevância na Pesquisa
698.1277%
采用ISOMET 热特性分析仪对废铸砂(WFS)、粉煤灰(FA)、聚苯乙烯(EPS)颗粒、水泥(可选)与水 按一定质量比例混合制成的抗冻胀、低导热性、轻质填料进行了导热系数测定,探讨了不同状态下(冻结与否)导热 系数与水泥、粉煤灰、EPS 颗粒掺入比、含水率以及龄期的关系,并与常规岩土材料进行对比,进行了变量权重的正 交分析,建立导热系数与不同组分含量关系的预测公式。试验结果表明,单因素变化时,EPS 颗粒含量、粉煤灰含量、 水泥含量的增加会不同程度地降低导热系数,有助于隔热与降低冻结深度;干密度和含水率的降低会减小导热系数; 龄期的增加会增加导热系数;主要变量因素降低填料导热系数的权重由大到小顺序为EPS 颗粒、粉煤灰和含水率;材 料的导热系数随水料比w/(10EPS+FA)的增加而增加;试验调查的填料导热系数在0.5~1.0 W/m⋅K 范围,低于常见岩土 材料的导热系数(1.0~2.0 W/m⋅K)。= The thermal conductivity is a critical parameter of infrastructure materials, which are used as frost-resistant fills in cold regions. The parameter is mainly determined by the material composition. A frost-resistant fill...

Probabilistic Determination of Thermal Conductivity and Cyclic Behavior of Nanocomposites via Multi-Phase Homogenization

Tamer, Atakan
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
695.18195%
A novel multiscale approach is introduced for determining the thermal conductivity of polymer nanocomposites (PNCs) reinforced with single-walled carbon nanotubes (SWCNTs), which accounts for their intrinsic uncertainties associated with dispersion, distribution, and morphology. Heterogeneities in PNCs on nanoscale are identified and quantified in a statistical sense, for the calculation of effective local properties. A finite element method computes the overall macroscale properties of PNCs in conjunction with the Monte Carlo simulations. This Monte Carlo Finite Element Approach (MCFEA) allows for acquiring the randomness in spatial distribution of the nanotubes throughout the composite. Furthermore, the proposed MCFEA utilizes the nanotube content, orientation, aspect ratio and diameter inferred from their statistical information. Local SWCNT volume or weight fractions are assigned to the finite elements (FEs), based on various spatial probability distributions. Multi-phase homogenization techniques are applied to each FE to calculate the local thermal conductivities. Then, the Monte Carlo simulations provide the statistics on the overall thermal conductivity of the PNCs. Subsequently, dispersion characteristics of the nanotubes are assessed by incorporating nanotube agglomerates. In this regard...

Thermal conductivity in high silicon cast iron

Gómez Saro, Albano
Fonte: Universidade de Cantabria Publicador: Universidade de Cantabria
Tipo: Trabalho de Conclusão de Curso
ENG
Relevância na Pesquisa
693.5175%
ABSTRACT: In this report the thermal conductivity of five cast irons with different composition is studied. The castings chosen for the project were a standard spheroidal graphite iron (SGI), and two SGI with high silicon contents, and two compacted graphite irons (CGI) with also high silicon contents. Some experiments were done for each studied cast iron as dilatometer, differential scanner calorimeter (DSC) and Laser flash. After the thermal study, a microscope analysis was done in order to obtain the nodularity, the graphite amount and the ferrite and pearlite amount of each cast iron. The goal of the project is investigate the thermal behaviour of casting with high silicon contents and find any kind of relation between the silicon content, the thermal conductivity and the nodularity. The results doesn´t report an important influence of the silicon content in the thermal conductivity. Studying the results it is concluded that in applications were high thermal conductivity is required, it is recommended cooling rates corresponding to thickness higher than 50 mm.; Ingeniería industrial

Experimental investigation of thermal conductivity coefficient and heat exchange between fluidized bed and inclined exchange surface

Stojanovic,B.; Janevski,J.; Stojiljkovic,M.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2009 EN
Relevância na Pesquisa
690.6938%
The paper presents experimental research of thermal conductivity coefficients of the siliceous sand bed fluidized by air and an experimental investigation of the particle size influence on the heat transfer coefficient between fluidized bed and inclined exchange surfaces. The measurements were performed for the specific fluidization velocity and sand particle diameters d p=0.3, 0.5, 0.9 mm. The industrial use of fluidized beds has been increasing rapidly in the past 20 years owing to their useful characteristics. One of the outstanding characteristics of a fluidized bed is that it tends to maintain a uniform temperature even with nonuniform heat release. On the basis of experimental research, the influence of the process's operational parameters on the obtained values of the bed's thermal conductivity has been analyzed. The results show direct dependence of thermal conductivity on the intensity of mixing, the degree of fluidization, and the size of particles. In the axial direction, the coefficients that have been treated have values a whole order higher than in the radial direction. Comparison of experimental research results with experimental results of other authors shows good agreement and the same tendency of thermal conductivity change. It is well known in the literature that the value of the heat transfer coefficient is the highest in the horizontal and the smallest in the vertical position of the heat exchange surface. Variation of heat transfer...

Thermal conductivity measurement of gas diffusion layer used in PEMFC

Radhakrishnan, Arjun
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
699.73734%
The objective of the present work is to develop an apparatus to measure the thermal conductivity of gas diffusion layer (GDL) as a function of temperature and compression, and also to develop an effective thermal conductivity (ETC) model to predict thermal conductivity of fibrous media as a function of compression. Thermal conductivity of GDL at different operating conditions is essential for accurate thermal modeling in a Proton exchange membrane (PEM) fuel cell stack. Steady state method of guarded hot plate method was used to perform the thermal conductivity measurements and the measurements were carried out on commercially available GDL samples - Toray and SGL (SIGRACET®). GDL thicknesses at different compressions were also measured to calculate the thermal conductivity of GDL at a given compression. Thermal conductivity of Toray was found to decrease with temperature while that of SGL was constant over temperature. Both Toray and SGL thermal conductivities were observed to increase with compression. Also, contact resistance between GDL-copper surfaces was found to decrease with compression for both Toray and SGL. Furthermore, the effective thermal conductivity model was used to estimate the thermal conductivity of the tested GDL samples at different compressions and was found to match pretty well with the experimentally determined thermal conductivity values.

Methods to characterize and enhance the through-thickness thermal conductivity of three dimensional polymer composites

Yu, Hang
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Relevância na Pesquisa
701.4214%
Advani, Suresh G.; Increased polymer composites are being used to replace traditional materials in modern structures and industrial applications due to their light weight and corrosion resistant features. However some of these devices and components are subjected to increasing thermal load and as polymer composites are poor conductors of heat, thermal management is critical. Thermal transport mechanisms are investigated and characterized when highly conductive fibers are embedded in three-dimensional polymer composites. Improved out-of-plane thermal conductivity of fiber reinforced polymer (FRP) composite materials will enable lightweight structures to integrate efficient thermal management. Different approaches have been explored to enhance out-of-plane thermal conductivity and address measurement issues associated with this class of composites, including Z-pin insertion and distribution, particle-fabric reinforcement and laminate stacking sequence design and some combinations of above factors. An approach in which a conductive coating is applied on the surface of composite samples to improve the through-thickness thermal conductivity of composites containing a small percentage of conductive fibers in the thickness direction is explored. A parametric study revealed that the thickness of the coating and the distribution of the conductive fibers play a crucial role in augmenting the heat transfer across the thickness of the polymer composite. For the enhancement of through-thickness thermal conductivity of nonwoven laminated composites...

Optimized design of nanofibers for low thermal conductivity in nanocomposites

Unni, Vineet
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Relevância na Pesquisa
698.1277%
Feser, Joseph P.; The design of efficient thermoelectric materials involves the reduction of thermal conductivity attributable to heat conduction by thermally generated elastic waves called phonons, without degradation of electrical conductivity. Improved scattering of phonons can be attained by introducing a small volume fraction of embedded nanoparticles inside a semiconductor alloy matrix material. Calculating the thermal conductivity tensor from microscopic principles requires knowledge of the scattering cross-sections spanning all possible incident elastic wave orientations, polarizations and wavelengths. In this thesis, analytical continuum mechanics is used to construct the scattering cross-section of incident elastic waves from embedded nanofibers where the waves have arbitrary orientation, polarization, and wavelength. The model is then incorporated using Boltzmann transport theory to predict the thermal conductivity tensor. The thermal model is used to study optimal methods of producing low thermal conductivity nanocomposites. We consider the specific case of Si 0.5 Ge0.5 alloy matrix materials as the active thermoelectric component and nanoparticle scatterers including Ni, Co, and Pt silicide compounds. The thermal conductivity tensor is studied as a function of fiber size...